A. Field of the Present Invention
The present invention relates to energy efficient, reflecting/transmitting corner cube arrays and, in particular, to incandescent lamps of the energy saving type wherein infrared energy is returned to the filament by such an array, allowing visible light to escape the envelope of the lamp.
B. Description of the Prior Art
Several attempts have been made to create an incandescent lamp which returns (reflects) a substantial portion of the infrared energy emitted by the filament back to the filament itself. This is accomplished by using the envelope of the lamp as a surface which will transmit visible light effectively unimpeded but which will substantially reflect infrared energy back to the filament.
In one such commercial construction, Duro-Test Corporation employs a lamp envelope which is coated with a metal film having a trademark Vistir. This energy saving lamp operates in the manner described above, i.e., it transmits visible light energy and reflects infrared energy back to the filament so that less energy is used in total to light the lamp than an ordinary incandescent lamp.
One difficulty with the Vistir-coated Duro-Test lamp is the requirement that the envelope be precisely shaped so that the infrared energy will reasonably accurately be returned to the filament.
It has been known to use corner cube reflecting surfaces in various applications to redirect light back in the direction of its source. It has also been proposed, such as has been disclosed in U.S. Pat. No. 4,612,473 to Nillsen, to use a plurality of dichroically structured corner cube reflectors to transmit visible light while reflecting infrared energy to the filament of an incandescent lamp. While Nillsen's proposal removes the requirement that the lamp envelope need be made accurately, his disclosure is limited to construction of a dichroic surface where his corner cubes are arranged in a triangular way (see his FIG. 2) which does not provide reflective surfaces designed for efficient infrared reflection. Nillsen's triangular method of joining the corner cubes will result in 50% of the rays incident on the corner cube missing the third corner so that they will not return to the filament of the lamp.